His brothers were César Henri, comte de La Luzerne, Naval Minister (1787-1790) and Anne-César, ambassador to the United States and to the court of London.

His studies at Collège de Navarre continued throughout this time, and he so distinguished himself that when, in 1762, Arthur Richard Dillon was appointed Archbishop of Narbonne, he chose La Luzerne for his Great Vicar.

On 24 June 1770 the king appointed La Luzerne to the very prestigious position of Duke-Bishop of Langres, (an ancient French peerage).

La Luzerne took his duties very seriously and invested heavily in renovations to church property, establishing seminaries, and conducting synods and assemblies.

He was elected president of the assembly (31 August 1789 - 9 September) but resigned within days in protest of a speech made by the marquis de Lally-Tollendall.

An excellent apologist and a lucid expounder of Catholic faith and Christian ethics, La Luzerne, like Denis-Luc Frayssinous, Talleyrand-Périgord and Bausset, was a belated representative of the old Gallicanism.